Beer Planet (www.beerplanet.eu) - if you spend 100 euros or more on beer, you get a bottle of Westvleteren 12 as a gift. Beer Temple is a good option. If you're a fan of lambics, go straight to the Cantillon brewery, easy walking distance from the midi station. There's also Beer Mania (www.beermania.be) and Delices et Caprices.

Those places should help fill your suitcase. If you have a car, there are more options, of course.

Thanks for the advice. I'll be on the train, so there's a limit to how much I can carry. I'll be passing through Brussel's at then end of this month, beginning of July en route to Amsterdam (from the UK) for work.